<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    *{
      margin: 0;padding: 0;
    }
    ul li {
      list-style: none;
      width: 200px;
      height: 50px;
      /* flex-shrink: 1; */
      /* flex-grow: 1; */
      flex: 1 1 200px;
    }
    /* li:nth-child(2) {
      flex-shrink: 0;
    } */

    ul{
      width: 700px;
      display: flex;
    }
  </style>
</head>
<body>
  <ul>
    <li style="background: rgb(235, 17, 17);">1</li>
    <li style="background: rgb(50, 226, 56);">2</li>
    <li style="background: rgb(16, 201, 218);">3</li>
  </ul>
</body>
</html>